Fresh Seawater Samples Research Articles

Investigations of Aerobic Methane Oxidation in Two Marine Seep Environments: Part 1—Chemical Kinetics

AbstractMicrobial aerobic oxidation is known to be a significant sink of marine methane (CH4), contributing to the relatively minor atmospheric release of this greenhouse gas over vast stretches of the ocean. However, the chemical kinetics of aerobic CH4 oxidation are not well established, making it difficult to predict and assess the extent that CH4 is oxidized in seawater following seafloor release. Here we investigate the kinetics of aerobic CH4 oxidation using mesocosm incubations of fresh seawater samples collected from seep fields in Hudson Canyon, U.S. Atlantic Margin and MC118, Gulf of Mexico to gain a fundamental chemical understanding of this CH4 sink. The goals of this investigation were to determine the response or lag time following CH4 release until more rapid oxidation begins, the reaction order, and the stoichiometry of reactants utilized (i.e., CH4, oxygen, nitrate, phosphate, trace metals) during CH4 oxidation. The results for both Hudson Canyon and MC118 environments show that CH4 oxidation rates sharply increased within less than one month following the CH4 inoculation of seawater. However, the exact temporal characteristics of this more rapid CH4 oxidation varied based on location, possibly dependent on the local circulation and biogeochemical conditions at the point of seawater collection. The data further suggest that methane oxidation behaves as a first‐order kinetic process and that the reaction rate constant remains constant once rapid CH4 oxidation begins.

Marine microbes rapidly adapt to consume ethane, propane, and butane within the dissolved hydrocarbon plume of a natural seep

AbstractSimple hydrocarbon gases containing two to four carbons (ethane, propane, and butane) are among the most abundant compounds present in petroleum reservoirs, and are introduced into the ocean through natural seepage and industrial discharge. Yet little is known about the bacterial consumption of these compounds in ocean waters. To assess the timing by which microbes metabolize these gases, we conducted a three‐phase study that tested and applied a radiotracer‐based method to quantify the oxidation rates of ethane, propane, and butane in fresh seawater samples. Phase 1 involved the synthesis of tritiated ethane, propane, and butane using Grignard reagents and tritiated water. Phase 2 was a systematic assessment of experimental conditions, wherein the indigenous microbial community was found to rapidly oxidize ethane, propane, and butane. Phase 3 was the application of this tritium method near the Coal Oil Point seeps, offshore California. Spatial and temporal patterns of ethane, propane, and butane oxidation down current from the hydrocarbon seeps demonstrated that >99% of these gases are metabolized within 1.3 days following initial exposure. The oxidation of ethane outpaced oxidation of propane and butane with patterns indicating the microbial community responded to these gases by rapid adaptation or growth. Methane oxidation responded the slowest in plume waters. Estimates based on the observed metabolic rates and carbon mass balance suggest that ethane, propane, and butane‐consuming microorganisms may transiently account for a majority of the total microbial community in these impacted waters.

Eppur si muove: many water column bacteria are motile

Models of chemosensory behaviour and micro- scale patchiness in the water column often assume that most or all suspended bacteria are motile. Yet direct observations on fresh seawater samples seem to indicate that only a few percent of suspended bacteria swim. Consequently, most experimental studies on the role of bacterial chemotaxis in the water column depend on pure strains of bacteria or on incu- bations enriched with organic substrates. Here it is shown that a large fraction (typically >20%) of the bacteria (in terms of direct counts) are, in fact, motile and show chemosensory behaviour. The discrepancy is due to the tendency of motile bacteria to attach rapidly to solid surfaces; in microscope preparations that are suited for observation of µm-sized par- ticles most motile cells will become attached within a few seconds.

Marine bacteriophage reproduction under nutrient-limited growth of host bacteria. I. Investigations with six phage-host systems

Bacteriophage reproduction was investigated with 6 phage-host systems (PHS) isolated from the North Sea near Helgoland, Germany, with the hosts adapted to growth at 6 or 0.6 mg organic nutrients 1-' For 5 of the PHS, similarities in production were observed to depend upon the time of infection during a transition period which included the last hours of the logarithmic growth phase and the first 1 to 2 d of the stationary growth phase of the host bacteria. Over this period the extent and/or the rate of phage production d-' decreased greatly. After longer incubation before addition of phage, the relative ability of host cells to propagate phage either ceased (3 PHS) or was regained (1 PHS) or remained the same as dunng the transition period in regard to final phage concentrations ( l PHS). The remaining PHS showed no phage reproduction at the low nutrient concentration. With phage-res~stant mutant bacteria serving as competitors for nutrients, phage production was drastically reduced. The present findings are in agreement with observations concerning concentrations of infective virions in fresh seawater samples. They failed, however, to provide evidence for the hypothesis that release of mature phage in starving marine bacteria is delayed until sufficient nutrients become available.

Laboratory measurements of ozone deposition to sea water and other saline solutions

Measurements of ozone deposition velocity to fresh seawater samples collected over the course of a year have been made using a static chamber technique. The magnitude of the ozone deposition velocity ( ca 0.01 cm s −1) was in broad agreement with the relatively few values reported in the literature. A strong correlation between ozone deposition and dissolved surfactant concentrations was found which is reflected in their similar seasonal trends. Stirring the water resulted in a significant increase in the rate of ozone uptake at the surface which suggests that wave motion may increase deposition velocity by constantly and rapidly replenishing the reactive surface organic layer.

Lead speciation in surface waters of the eastern North Pacific

Titrations using differential pulse anodic stripping voltammetry (DPASV) to detect electroactive lead were carried out on fresh seawater samples and on samples stored acidified to determine the extent of lead complexation in the eastern North Pacific. Results of these analyses on surface water samples indicate total dissolved lead concentrations between 17 and 49 pM. The inorganic or DPASV labile fraction is 30–50%. Titration with lead yielded data consistent with one class of organic ligand(s), present at low concentration (between 0.2 and 0.5 nM) with a mean value for a conditional stability constant with respect to inorganic lead of log K′ cond=9.7. The presence of this ligand, together with the various inorganic ligands in seawater, gives rise to a concentration of free ionic lead of ∼ 0.4 pM.

Effect of toluene exposure time and concentration on induction of high affinity values for toluene oxidation by bacteria of estuarine seawater samples

Upon amending fresh seawater samples with toluene, metabolism began immediately; autoradiography indicated that a minimum of about 7 % of the bacteria were responsible. Rate of toluene metabolism increased with time, maximal rate of increase occurring about 48 h following exposure. There was no concomitant increase in bacterial populations and, consistent with observations of marine isolates in predator-free systems, the increase in rate was interpreted as induction. Induction followed saturation kinetics as might be expected if the rate of inducer penetration also followed saturation kinetics; Kind observed was the very small value of 1.9 yg 1-l, but was consistent with Michaelis constants for toluene transport observed in other studies.

Evidence for a Terpene-Based Food Chain in the Gulf of Alaska

A mixture of C-terpenes was prepared from conifer seedlings and introduced into fresh seawater samples taken near Seward, Alaska. Initial rates of oxidation by the indigenous bacteria were linear and faster than the rates of toluene oxidation. Turnover times were 4 to 19 days. Autoradiographic measurements with H-terpenes indicated that at least 10% of the 0.6 x 10 to 2.7 x 10 bacteria per liter present could catabolize terpenes. The rate of terpene oxidation, 24 mug of terpenes per g of cells per h with 3 mug of terpenes added per liter, was a constant function of bacterial biomass. The specific affinity of the process was estimated to be between 8.1 and 81 liters/g of cells per h, indicating a high state of induction and the probable presence of terpenes. Terpene-oxidizing bacteria were grown on [C]alanine and added to fresh seawater samples. Transfer of the bacterial radioactivity into larger particles at a rate of 146 pg/liter per h from the 2.3 x 10 organisms added indicated that any terpenes present would participate in the food chain.